1. Field of the Invention
The invention relates to depth sounders and refers more specifically to a signal processor unit for use in conjunction with a ship's sonar which facilitates multiple remote depth displays in either digital or analog form and which includes depth alarm, lost echo, alarm set display, and scale expanding capabilities.
2. Description of the Prior Art
In the past, sonar-type depth sounders have been known which have produced ultrasonic pulses from a transducer mounted on the bottom of a boat and received corresponding ultrasonic pulses reflected from the bottom of a body of water. The circuitry of the prior depth sounders has been such that the time between a transmitted pulse and an echo or reflection of the same pulse has been used to determine the depth of the body of water, since the time of travel of the ultrasonic signals in water is known.
Displays for such prior depth sounders have in the past included motor driven flashers wherein an electric motor has been driven at a constant speed to rotate an arm mounted on the motor shaft and wherein a light-emitting diode or a neon lamp at the tip of the arm has been caused to flash on transmission of the main pulse and again on receipt of the echo signal. Such display devices have also been used to provide a permanent record with the motor driven arm traveling over a moving strip of paper, which paper is electrically discolored by an electrical pulse occurring concurrently with the transmitted pulse and each echo as received. Meter displays have also been used in prior depth sounders which produce an average current through a microammeter in response to integration of pulses received from the sonar, which pulses are started and stopped with the sonar main pulse and echo.